The present invention is directed to a switching regulator having at least one regulated output voltage.
A switching regulator is disclosed in U.S. Ser. No. 941,448 filed Oct. 26, 1992. In this switching regulator, a device for peak value current limitation is provided, whereby a comparator has one input connected to a reference voltage and the other input connected to a current-measuring resistor. A delta voltage source is arranged in series with the current-measuring resistor.
The delta voltage source supplies an external, synchronous delta signal that is superimposed on the current-meter voltage. Such a superimposition of an external, synchronous delta signal, (disclosed in German Published application 26 13 896) is advantageous in the evaluation of the current-meter voltage with the use of a comparator. On one hand, a defined switch criterion is acquired; on the other hand, the stability in the sub-harmonic range is enhanced.
In a version of the known converter, the multiplier resistor simultaneously serves as actual value generator of a current regulator having superimposed voltage regulation, whereby the actual value of the voltage is the rated value of the current regulation. In such a current mode regulation, a current signal, that serves as turn-off criterion for the pulse duty control, is necessary that is made available to the control circuit as voltage drop-off across a current-measuring resistor or as load voltage of a current transformer.
European reference EP 0 302 433 A1 discloses that forward converters or reverse converters should be provided with current-dependent magnet component parts, for example with what are referred to as non-linear inductors whose inductance decreases with decreasing DC load.
In the reverse converter, a storage transformer having a current-dependent ferrite core effects a noticeably extended current conduction time in the secondary circuit given a weak load. This improves to a considerable extent various properties of the converter, particularly the smallness of the superimposed alternating voltage and the radio interference suppression.
In the forward converter, use of current-independent storage inductors in the low-ass filter that forms the average value is expedient when, for example, a gap-free operation is to be avoided given a great load range and a plurality of output circuits. Such a current-dependent magnet component part also allows extremely low thresholds, so that the internal losses in the current supply device can be kept low.
When a converter is only slightly loaded at the output, then there is a comparatively small voltage drop across the current-measuring resistor. When the level of the current-meter voltage serving as a turn-off criterion is selected so high that an adequately exact turn-off is guaranteed given low-load operation, there is a correspondingly high dissipated power at the current-measuring resistor given maximum nominal load.
In order to utilize the advantages of a magnet component part having current-dependent inductance in combination with the advantageous voltage regulation with underlying current regulation (current mode regulation), then the problem arises that the current-meter voltage and the chronological rise of the current-meter voltage given low load is even lower than when a current-independent inductance is used.